Electrolyzing fused baths



Jan, 27, 1925. 1,524,268

R. J. MCNITT ELECTROLY ZING FUSED BATHS I Original Filed Feb. 2, 1921 2Sheets$heet l J 27, 1925. 1,524,268 R. J. MCNITT BLECTROLYZING FUSEDBATHS Original Filed Feb. 2, 1921 2 Sheets-Sheet 2.

be mentioned the following:

Patented Jan. 27, 192 5.

UNITED STATES PATENT oi-"Pica.

ROBERT J. MGNITT, OF PERTH AMBOY, NEW JERSEY.

ELECTROLYZING FUSED BATES.

Application filed February 2, 1921, Serial No. 441,921. Renewed April 4,1924.

and State of New Jersey, have invented certain new and usefulImprovements in Electrolyzing Fused Baths, of which the following is aspecification.

My invention pertains to electrochemical processes operating with fusedelectrolytes, and has for its purpose the elimination or reductionofimperfections existing in such processes. Among these imperfections may1st. The application of heat from external sources is not advantageouslymade, and in attempting to maintain thermal equilibrium by -means of theelectrolytic current there occur excessive energy losses, and thoseconditions favorable to high yields (current density and electrodespacing) are sacrificed. Where units are operated electrically in seriesas is customary, the'cur rent isadjusted to maintain a favorabletemperature in the coldest unit, that is the unit operating with highestenergy efliciency; and in order to prevent excessive temperature inother units, it is customary to shunt a portion of the current aroundthese units through an external resistance, to! disconnect the hot unitsfrom the circuit from time to time, to change the electrode spacing, tocirculate cooling fluids through ducts in the electrolyte or furnacewalls, or to vary the rate of heat radiation from external surfaces.These methods of control'result in loss of power, loss of production,unfavorable conditions for high average yields, and high costs forattendance and maintenance 2nd. In the operation of units connectedelectrically in multiple, it is difficult to maintain proper division ofthe electric current, on account of the temperature resistancecharacteristic of-the fused electrolyte.

After the current has been carefully ad justed, owing to a slight changein radiation constant or operating efficiency one unit may tend toCl'llll ofl' w1th consequent 1ncrease in the electrolyte resistance anda diversion of current to other units. One or more of these other unitswill warm up under the additional current with corresponding reductionin the resistance of their electrolytes. Hence more and more of thecurrent will be divertedfrom'the cold unit electrodes with largersurfaces and low re-' sistance it has been considered impracticable tooperate more than one electrochemical unit in a single cell, or tooperate individual cells in multiple except in a multiple seriesarrangement, where a sufficient number of units are in series, so thatthe average resistance characteristics of all parallel branches shall beapproximately the same.

3rd. The electrolye is not maintained in such condition as to uniformityof constituents, temperature and purity as is necessary to lnsureuniformly high ampere yields. It is customary to allow impurities toaccumulate until the yield falls below i the economic limit, whereuponthe electrolyte is removed, and the cell cleaned and refilled with freshelectrolyte; a method of operation which is costly in both labor andmaterials, and which results in relatively low average yields. Also, dueto the tendency to accumulation of impurities, all materials put intothe bath must be as pure as possible. l/Vhere mixed baths or fluxingagents are used it is difficultto maintain in all units the mostfavorable mixtures of constituents. Generally it is necessary to makefrequent analyses of the bath in. each unit, and, treating each unitseparately, to add such amounts of the various materials as aredetermined to be necessary.

4th. On account of structural limitations and operating difliculties thesize of the individual unit used in these processes is small, and theenergy lost through radiation and conduction is great in comparison withthe energy consumed in useful work. Also the cost of operating andmaintaining numerous small units is high.

Now the improvement which I have made reduces or eliminates theseimperfections and consists in its preferred embodiment:

In causing the fused electrolyte of proper (constitution, temperature,and purity to flow to each electrochemical unit, in excess of the amountrequired for electrolytic deoutside the zone of elctrolyticaction, and

2 cell wall are made of graphite and are re- I trolyzing units; and

submitting same to purification, replenishment, the application of heat,cold, or such I additional treatment as may be necessary totproduce anelectrolyte of proper constitution, temperature and purity; and cansingthe latter to again flow in excess to each unit as described before.

By way of illustration I shall describe my invention asapplied to aprocess of electrolyzing fused sodium chloride in units consisting ofvertical electrodes separated by a porous partition or diaphragm, andfor assistance to a clear understanding of the invention reference ismade to the accom panying drawings, in which the figures arediagrammatic in character and wherein:

Fig. 1 is a vertical longitudinal view,

partly in section along line 11 of Fig. 2,

I of a typical installation for the above pur- )oses. 1 Fig. 2 is a planview of the same;

Fig. 3 is a partly sectional View along the central line 3-3 of Fig. 2;

Fig. 4 is a transverse vertical section on line 4-4 of Fig. 2; v

Fig. 5 is a transverse vertical section on a somewhat larger scale ofone of the elec- Fig. 6 is a longitudinal vertical section on a somewhatenlarged scale of one ofthe electrolyzing units.

The illustrated installation comprises a multiplicity of electrolyzingunits 10 arranged in multiple electrical connection with a source ofcurrent 11, and are grouped together to reduce the external heatradiating andconducting surfaces. The walls of the cells l2 inwhlch'theunits are located are preferably constructed of refractory brick andfireclay shapes and are preferably surrounded by thermal insulatingmaterial, as Ifor-example bricks 13 made from kieselu r.

O The anodes 14 which form part of the spectively connected with thesource of electrical energy 11 through graphite conhoods 21 surmountingthe cathodes. In turn these hoods are supported by pipes 22 throughwhich the metallic sodium which collects in Lhe hoods in operation maybe withdrawn. Inwardly extending collars 21 centrally of the hoodprovide passages between the upper and lower levels of the cells.

The chlorin gas develo ed in the electrol sis is removed throng pipes23. p

The bottoms 24 of the cells converge as shown and open into a duct ortrough 2b running lengthwise of the installation, there being shown oneof these ducts for each of the two rows of cells. Each duct 25 opens atone end thereof into an electrolyte reservoir 26 and the two reservoirs26 are in c0mmunication at or near their bottoms through a cross-passage27 (Fig. 4). In each reservoir 26 a pump 28 is provided,

the outlet passage whereof leads to respective filter chambers 29. Eachfilter 29 has an outlet pipe 30 communicating with a central reservoir31.

A suitable pump 32 in reservoir 31 has its inlet side open to theelectrolyte in the reservoir while its outlet connects through pipe 33with acell-supply duct or manifold 34 which lies in a channel in the topof the brickwork between and above the two rows of cells. Branch pipes35 distribute the ,electrolyte to the individual cells, regulation ofthe flow through the respective branch pipes being effected by means ofthe valves 36. The electrolyte is preferably introduced into the cell attwo points on each side thereof, a portion entering at the top of theanode 14 through pipes 37 (Fig. 6) and a portion entering near the topof the bath through the pipes 38. The relative flow through pipes 37 and38 is adjusted by suitable devices, not shown, such as deflectors in thebranch pipes 35.

For supplying additional heat to the electrolyte flowing to the units,each of the individual feed pipes 37 may be provided with an electricalresistor 39. For the purpose of extracting heat from the electrolyte asit passes through the branch ducts, the latter are provided at theirupper portions with suitable water-jackets 40 (Fig. 5)

Beyond the branch pipes of the last cells the manifold 34 makes a returnbend, and extends rearwardly beneath the cell-supof gas or oil burners47.

plying portion of the same, through the central reservoir 31 and into anelectrolyteheating retort 41. The heating means for this retort may be agas or an oil burner, indicated at 42. Through a valved outlet 43 theelectrolyte which "is not diverted to the cells 10 is returned. to thereservoir 31- :tor recirculation, valve 44 in the section of themanifold extending into the retort 41 being partly orentirely closed. Itsubstantial reheatingot the electrolyte is necessary, valve 44 is openedand valve 43 is partly or entirely closed.

Arranged near the reservoirs 26 and communicating respectively therewithare retorts 45 into which the solid replenishing materials, for examplecommon salt with small quantities of fluxing agents, are introducedthrough hoppers 46, and in which such materials are fused and purified.The retorts may be externally heated by means For purilying thematerials, the latter in a fused state are passed through speciallow-voltage electrochemical units 48, shown submerged in the fused bathsin retonts 45, and provided with insoluble or removable anodes. .Thefused replenishing materials are discharged from units 48 through pipes49 into reservoirs 26 where they mingle with the residual portion of theelectrolyte therein, and are filtered with the latter.- 1

For maintaining an elevated temperature in the fused electrolyte in thereservoirs 26, an electrical resistor 50 maybe located along the bottomsthereof andthe bottom of the cross duct'27ewhich connects the reservoirs26. The terminals of the resistor are indicated at 51. Similarly, theduct 25 -may be provided with an electrical resistor 52 for maintainingthe fused electrolyte therein at an elevated temperature.

In using the apparatus described for carrying out my process, afused'electrolyte of proper temperature, purity and constitution, forexample sodium chloridand such fluxing agents as may be preferred, ispumped from reservoir 31 through the manifold 34 to each unit, in excessof the amount required for electrolytic decomposition. The flow of theelectrolyte to the various units 10 is regulated by the valves 36 in thebranch ducts 35, and the temperature of the entering electrolyte isregulated by means of the respective electric heating elements 39 (Fig;5). By this regulation the tem- V perature ofthe electrolyte undergoingelectrolysis is held at the point favoring highest yields. Also a properdivision of electric current is maintained between the various unitsconnected in multiple.

The electrolyte is circulated through the units in such manner (seearrows in Figs.

'5 and '6) that solid impurities such as particles of carbon, carbides,iron, calcium, magnesium, copper, sand 'and fireclay, as well asimpurities in solution, such as the metallic chlorids, are taken up bythe residual portion of the electrolyte (i. e. the portion notdecomposed) and removed from the Zone of electrolytic action. Thisresidua1 portion of the electrolyte laden with impurities passes throughthe open "bottom of each unit into one of the ducts 25 where it uniteswith the residual portions from the other units, and by these ducts 25the electrolyte is conveyed to the reservoirs 26. In the latter arefacilities toixremoving impurities from the electrolyte. Purificationmay consist in chemical treatment, or electrolysis in a speciallydesigned unit, to separate out impurities from solution, or it mayconsist merely in settling or filtering out of the solid impurities. Thedetailed method of purification depends on the nature of the impurities,which in turn depends upon the purity of the materials used forreplenishment, and the nature of the materials used in the constructionof the supporting structure and linings of the cell surrounding theunit, as well as upon the skill of the operator. In general, mechanicaltreatment is sutficient and accordingly I have shown a filter 29 in eachreservoir 26 through which the electrolyte is forced by the pumps 28.The filters may beconstructed of wire cloth, perforated metal, coke,charcoal and similar materials. From the filters 29 the purifiedelectrolyte passes into the central reservoir 31 for recirculation.

The facilities for fusing and mixing the materials supplied as requ1redfor replenishing the electrolyte are preferably grouped together withthe units as shown, and where the number of units is suflticient theremay be facilities for purifying these materials. In the exampledescribed the replenishing materials, mostly common salt with smallquantities of fluxing agents are fused in the'retorts 45, being fedsolid thereto from thehopper46 (Fig.1). The purification treatment ofthe replenishing materials is. here illustrated as effected byelectrolyzing the fused material in a special low voltage unit 48, theanodes of which are insoluble or removable. By this treatment oxygenbearing impurities are broken down and prevented from entering theregular process and attacking the permanent graphite electrodes. Theunits 48 are shown sub merged in the tusedbaths in retorts 45.

The fused replenishing materials are discharged trom the units 48through the conduits 49 into the reservoirs 26 where they mingle withthe residual portion of the electrolyte and are filtered with thelatter. The temperature of the fused electrolyte in the reservoirs 26 ismaintained at a suitable point by the generation of heat in theelectrical resistors 50 and 52 located at the bottoms" of the reservoirsand the ducts 25 and 27 The purified and replenished electrolyte isdischarged from the filters 29' into the discharged through valve 44into retort 41 (Figs. 2 and 3) where heat is added, and the hotelectrolyte discharged by pipe 53 into reservoir 31 from which it isagain pumped to the various units through the manifold 34.

By the addition of heat to the electrolyte in retorts 45 and 41 and theresistor in duct 27, it is possible to maintain thermal equilibrium inthe system and still opcrate the units with a current density andelectrode spacing most favorable for'maximum yields. This additionalheat replaces a considerable portion of the total energy losses andresults in 'a saving in electrolytic power by reducing the operatingvoltage to a point as near as possible to the decomposition voltage.

Where heat is added by the combustion of fuels, retorts 45-and 41 shouldbe made wholly or as to linings from calorized steehmiekel-chromium orother suitable alloys. As the quantity of exit gases from the retortsmay be considerable and as they leave the heating surfaces at a hightemperature it is economical to pass them through some form ofeconomizer (not shown), as for example a steam boiler.

If the cost of electrical power' is relatively low, heat may be obtainedfor fusing the replenishing materials and maintaining temperatureequilibrium by applying the power directly or indirectly throughresistors in retorts 45 and 41 or in the reservoirs 26 and 31-. I Theregulation oftemperature of the electrolyte entering each unit isbrought about by adding or extracting heat at some point between thecontrol cock 36 of each unit and the point where the electrolyte entersthe chamber surrounding the unit. This heat is added by applyingauxiliary electric power, or by the combustion-of gas or oil. In theembodiment illustrated in the drawings, it is obtained through theelectrical resistors 39 -.(Fig,- 5) in each branch duct 35 whichconnectseach cock 36 with the chamber surrounding the unit. Where oil or gasfuel is used a .small'coil or r e.-'

tort (not shown) of sufiicient heating surface is inserted between eachcock and the corresponding branch duct, and the entering electrolyte ismade to flow through this coil or retort while flames are projectedagainst the external surface. Heat is extracted by wa ter-cooling. Inthe example illustrated, the upper portion of each branch duct 35 issurrounded by a Water-jacket 40 (Fig. 5) so proportioned that thetemperature of the flowing electrolyte may be reduced without risk offreezing or solidification.

By the manner of flow through manifold 34, the electrolyte enters thecontrol cook 36 of each unit at practically the same temperature. Alsothe constitution of the electrolyte is practically uniform in all units.These two facts make it possible to control most units by merelyregulating the rate of flow of the entering electrolyte. In units havingabnormal radiation or efiicien'cy characteristics, however, it isadvantageous to be able to regulate the temperature of the enteringelectrolyte.

By virtue of the control obtained through regulation of the temperatureand rate of fiow of the entering electrolyte, it is possible to adjustthe electrolytic current for average conditions and to run for a longperiod without readjustment. The excess heat developing in any unittendin to run warm is carried by a relatively arge flow of slightlysuperheated electrolyte into the duct 25, where it warms up the chilledelec trolyte returning from units which tend to run cold. This thermalequalizing effect is most advantageous in saving energy and instabilizing the system, thus reducing the attendance required.

The circulation of the electrolyte through each unit should be such asto insure that the purest electrolyte shall always be present in theelectrolytic zone, that im urities shall be prevented from entering t eelectrolytic zone and shall be removed to the reservoirs 26 with theresidual electrolyte. The circulation should also facilitate thetemperature control of the electrolyte of each unit. In the exampledescribed, this is accomplished by causing a portion of the electrolyteto enter at the top of the anode and a portion to enter near the top ofthe bath (Figs. 5 and 6). By adjusting. the relative flow entering atthese ints, which is accomplished by suitable de ectors in the ducts 35leading from the cocks 36 to each electrolytic chamber, and by properlyproportioning the various openings and passages this method ofcirculation is very satisfactory.

The auxiliary electric heat is adVa'ntn-' geously applied in themanifold 34 and in the duct 25 to-facilitate starting up of the systemand to maintain it in smooth operation.

The application of my invention to the process described above carriesthe following improvements:

(l) A large reduction in energy losses is effected;

(2) The electrolytic power: used per lb. of product is reduced;

(3) The current density, electrode spacing, and the condition of theelectrolyte as to constituents, temperature and purity are ideal foruniform and continuous high yields;

(4) The units are operated entirely satisfactorily in multiple, which inturn permits them to be grouped in the compact simple systemillustrated;

(5)The interruptions required for chang-' ing the diaphragm and forcleaning are materially reduced;

(6) The labor and attendance required in the operation are minimized;

(7 By continuous operation under uniform conditions there is less wearand tear,

and by fusing the replenishing materials in one place and handling themolten bath mechanically both labor and energy are re;

duced. I

I do not limit my invention to the arrangement and details described, asit may be applied with advantage to any arrangement of units or to asingle isolated unit. The electrochemical units may be located in acommon bath or separated by cell partitions. Likewise the purifying andtreating equipment may be contained in a common bath with theelectrochemical unit or units, or may be located in a separatecompartment as described above.

The operation of purification and treatment of the electrolyte may bedivided, a part of the operation, as for example settling and filtering,being carried on in connection with the units, while special treatmentis carried on continuously or in batches, in a special purificationplant isolated from the units. Likewise the preparation of the replenishing materials may be? carried on in connection with the units .asdescribed or may be done in a separate plant. v

' The circulation of the electrolyte may be continuous or intermittent.Each unit may have an independent circulation and purification system,or a number of units may be connected to a common system. Theelectrolyte may be made to flow to two or more units simultaneously or'to one after the other in succession. The various units may receiveelectrolyte from separate branches of the main duct, or the electrolytemay pass through one unit after the other in series.

In the latter case the regulation of rate of flow through any unit issecured by passing more or less of the main stream around the unitthrough a by-pass.

Where units are in series electrical con- .nection and receiveelectrolyte from a common source it may be necessary to avoid annoyancefrom cross currents by breaking the continuity of the electrolyte streamflowing to and from the units by means of a cock with an oscillatingdeflecting vane, a rotating disk or screw, a duplex tilting bucket, orother appropriate device.

I claim 1. The hereindescribed process of electrolyzing fused baths,comprising causing a fused electrolyte to flow in excess through anelectrochemical unit; controlling the operating temperature of said unitby regulating the temperature and rate of flow of the electrolyte;regenerating the undecomposed portion of the electrolyte at a pointoutside the zone, of electrolytic action, and returning the same to theelectrochemical unit.

2. Process according to claim 1 in which the electrolyte is caused toflow repeatedly through a plurality of electrochemical units in the sameelectrical circuit.

3. Process according to claim 1 in which the electrolyte is caused toflow repeatedly through a plurality of electrochemlcal units Ielectrically connected in multiple.

4. The hereindescribed process of electrolyzin fused baths, comprisinggrouping a plurality of electrochemical units in close proximity to eachother to minimize loss of heat by radiation; causing a fused electrolyteto flow in excess through said units; collecting the excess electrolyteat a common point outside the zone of electrolytic action; supplyingheat to the electrolyte at the said point; and returnin the electrolyteto the said units in cyclic ow.

5. The hereindescribed process of electrolyzing fused baths, comprisinggrouping a plurality of electrochemical units in close proximity to eachother to minimize loss of heat by radiation; causing a fused electrolyteto flow in excess through said units; 001- ROBERT J. MoNITT.

